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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "content/renderer/gamepad_shared_memory_reader.h"
#include "base/debug/trace_event.h"
#include "base/metrics/histogram.h"
#include "content/common/gamepad_messages.h"
#include "content/public/renderer/render_thread.h"
#include "content/common/gamepad_hardware_buffer.h"
#include "ipc/ipc_sync_message_filter.h"
namespace content {
GamepadSharedMemoryReader::GamepadSharedMemoryReader()
: gamepad_hardware_buffer_(NULL) {
memset(ever_interacted_with_, 0, sizeof(ever_interacted_with_));
CHECK(RenderThread::Get()->Send(new GamepadHostMsg_StartPolling(
&renderer_shared_memory_handle_)));
// If we don't get a valid handle from the browser, don't try to Map (we're
// probably out of memory or file handles).
bool valid_handle = base::SharedMemory::IsHandleValid(
renderer_shared_memory_handle_);
UMA_HISTOGRAM_BOOLEAN("Gamepad.ValidSharedMemoryHandle", valid_handle);
if (!valid_handle)
return;
renderer_shared_memory_.reset(
new base::SharedMemory(renderer_shared_memory_handle_, true));
CHECK(renderer_shared_memory_->Map(sizeof(GamepadHardwareBuffer)));
void *memory = renderer_shared_memory_->memory();
CHECK(memory);
gamepad_hardware_buffer_ =
static_cast<GamepadHardwareBuffer*>(memory);
}
void GamepadSharedMemoryReader::SampleGamepads(WebKit::WebGamepads& gamepads) {
WebKit::WebGamepads read_into;
TRACE_EVENT0("GAMEPAD", "SampleGamepads");
if (!base::SharedMemory::IsHandleValid(renderer_shared_memory_handle_))
return;
// Only try to read this many times before failing to avoid waiting here
// very long in case of contention with the writer. TODO(scottmg) Tune this
// number (as low as 1?) if histogram shows distribution as mostly
// 0-and-maximum.
const int kMaximumContentionCount = 10;
int contention_count = -1;
base::subtle::Atomic32 version;
do {
version = gamepad_hardware_buffer_->sequence.ReadBegin();
memcpy(&read_into, &gamepad_hardware_buffer_->buffer, sizeof(read_into));
++contention_count;
if (contention_count == kMaximumContentionCount)
break;
} while (gamepad_hardware_buffer_->sequence.ReadRetry(version));
UMA_HISTOGRAM_COUNTS("Gamepad.ReadContentionCount", contention_count);
if (contention_count >= kMaximumContentionCount) {
// We failed to successfully read, presumably because the hardware
// thread was taking unusually long. Don't copy the data to the output
// buffer, and simply leave what was there before.
return;
}
// New data was read successfully, copy it into the output buffer.
memcpy(&gamepads, &read_into, sizeof(gamepads));
// Override the "connected" with false until the user has interacted
// with the gamepad. This is to prevent fingerprinting on drive-by pages.
for (unsigned i = 0; i < WebKit::WebGamepads::itemsLengthCap; ++i) {
WebKit::WebGamepad& pad = gamepads.items[i];
// If the device is physically connected, then check if we should
// keep it disabled. We track if any of the primary 4 buttons have been
// pressed to determine a reasonable intentional interaction from the user.
if (pad.connected) {
if (ever_interacted_with_[i])
continue;
const unsigned kPrimaryInteractionButtons = 4;
for (unsigned j = 0; j < kPrimaryInteractionButtons; ++j)
ever_interacted_with_[i] |= pad.buttons[j] > 0.5f;
// If we've not previously set, and the user still hasn't touched
// these buttons, then don't pass the data on to the Chromium port.
if (!ever_interacted_with_[i])
pad.connected = false;
}
}
}
GamepadSharedMemoryReader::~GamepadSharedMemoryReader() {
RenderThread::Get()->Send(new GamepadHostMsg_StopPolling());
}
} // namespace content
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